The present invention is directed to a combined filter and sampler. In particular, the present invention is directed to a combined respiratory filter and sampling device which provides good filtering characteristics and improved sampling'capabilities in a single device.
Known air sampling methods for predicting human exposure include several techniques. Passive samplers are typically patches or disks which can be pinned to workers' clothing or affixed to structures. These samplers operate by absorbing materials brought to them by air currents and by diffusion through the air. No controls or measures of the airflow are available, so results will depend on where the sampler is placed and how it is used. Therefore, human exposure, and in particular respiratory exposure, to particle-laden flows can be misleading because the particle trajectories for a passive sampler will differ from trajectories where air is respired.
Active samplers typically consist of a fixed flowrate pump, filter, a pre-filter if desired, and a power supply. The pump draws air through the filter at a prescribed, constant rate for a given period. Human respiratory exposures are estimated from the levels of contamination that remain trapped on the filter. If particle-laden flows are to be analyzed, a cyclone device can be placed ahead of the filter. The cyclone selectively prevents particles above a given size from entering the filter.
Generally, two types of active samplers are available: high volume and personal. Personal air samplers are typically designed to be portable and usually consist of a pump and a filter in combination. The pumps draw 0.5-2.0 liters per minute through tubular filters. The filters can be pinned to a user's lapels, and the pump hung from a belt. High volume air samplers draw much higher flowrates of air, but require large power supplies and are typically fixed in position.
Existing active samplers, however, also have their own shortcomings. Active samplers are designed to estimate the average concentration of contaminants in the air, and not what a person in such an environment would have respired. Existing personal air samplers often draw an order of magnitude less air than a human would and are not positioned at the face, where actual exposure would occur. Active samplers work well when contaminants are vapors and exposure is constant and uniform, but during episodic or non-uniform exposure conditions, these samplers may not accurately portray the levels of exposure during the workday. Additionally, high volume air samplers are not suitable for environments where the worker is in motion over an extended area.
Several conventional mask filters are commercially available to trap contaminants and prevent their respiration. Conventional mask filters are, however, constructed with a single purpose in mind, to absorb as much material as possible in the most cost effective manner possible. These filters do not have the dual purpose of providing both an adequate respiratory filtering mechanism and providing the filtering capability in a structure that optimizes the way materials are trapped by the filter to enable accurate and efficient subsequent chemical analysis. Additionally, conventional mask filters are not designed for ready disassembly into component parts for chemical analysis.
Many existing mask filters are rather large or bulky due to the absorption materials used and the way in which they are arranged. This leads to filters which are heavy and either cumbersome or uncomfortable for a user particularly over long periods of time. As a result, a user may choose to forego the protection that such mask filters provide rather than tolerate these inconveniences.
It is apparent, therefore, that there exists a need for a combination respiratory filter and sampling device that provides filtering capabilities at least equal to existing filters while at the same time providing sampling capabilities far superior to known sampling devices.